Technical Abstract:
Avian tumor viruses (ATVs) can cause a variety of neoplastic diseases in poultry. ATVs belong to two major families of viruses: a) retroviridae, and b) herpesviridae. Lymphomas caused by avian retroviruses and herpesviruses are the most common virus-induced neoplastic disease condition of chickens. Retroviral lymphomas are caused by avian leukosis virus (ALV) or by reticuloendotheliosis virus (REV), whereas Marek's disease (MD) lymphoma is caused by a herpesvirus (MDV). A neoplastic disease of turkeys known as lymphoproliferative disease that has been described in Europe and Israel is induced by another retrovirus distinct from both the ALV and REV groups. Because ALV, REV and MDV are all widespread and infection in the absence of tumor formation is common, virologic and serologic criteria, such as assays for virus, antigens or antibodies may not be particularly helpful in diagnosis of tumors. However, the availability of sensitive and specific tests for detection of ATV infection is considered an integral part of any successful program to control disease. For instance, virological and serological assays for detection of ATV infection are very useful in identification and classification of new isolates, surveillance of pathogen-free and other breeder flocks for freedom of virus infection, establishing infection with one virus and exclude others, and in safety testing of vaccines.